1. Field
The present teaching relates to a light source apparatus, an optical apparatus, an exposure apparatus, a device producing method, an illumination method, an exposure method, and an optical apparatus producing method. More specifically, the present teaching relates to an illumination optical system of an exposure apparatus which is used to produce devices such as semiconductor elements, imaging elements, liquid crystal display devices, thin-film magnetic heads, etc., through a lithography process.
2. Description of the Related Art
Conventionally, in an exposure apparatus which is used to produce semiconductor elements, etc., a circuit pattern formed on a mask (reticle) is projected and transferred onto a photosensitive substrate (for example, a wafer) via a projection optical system. A resist coated on the photosensitive substrate is exposed through projection exposure via the projection optical system, and thus a pattern of the resist (resist pattern) corresponding to a pattern of the mask (mask pattern) is obtained. The resolving power (resolution) of the exposure apparatus depends on the wavelength of an exposure light (exposure light beam) and the numerical aperture of the projection optical system. Therefore, in order to improve the resolving power of the exposure apparatus, it is required to shorten the wavelength of the exposure light and to increase the numerical aperture of the projection optical system.
From the viewpoint of optical design, it is generally difficult to increase the numerical aperture of the projection optical system to a predetermined value or more. Therefore, it is necessary to shorten the wavelength of the exposure light. In view of this, attention is directed to an EUVL (Extreme UltraViolet Lithography) technique, which uses an EUV light (Extreme UltraViolet light or light beam) having a wavelength of approximately 5 nm to 20 nm, as a next-generation exposure technique (exposure apparatus) to be used for patterning semiconductor elements. In the case of using the EUV light as the exposure light, any usable light-transmissive optical material is not available. Therefore, the EUV exposure apparatus uses a reflection-type optical integrator, a reflection-type mask, and a reflection-type projection optical system.
For an ordinary exposure apparatus not limited to the EUV exposure apparatus, it is desirable to uniformize the light intensity distribution formed in a pupil of the illumination optical system (also referred to as “pupil intensity distribution” hereinbelow). The present applicant proposes a technique of forming an almost uniform pupil intensity distribution in an illumination pupil by elaborating the corresponding relation between a plurality of first mirror elements in a first fly's eye optical member and a plurality of second mirror elements in a second fly's eye optical member in the reflection-type optical integrator (see, United States Patent Application Publication No. 2007/0273859).